| The phenomenon of the resistance of metallic mercury suddenly dropped to zero at 4.2K found by Dutch scientist Onnes in 1911 that was called zero resistance of superconducting material.The Meissner effect with complete diamagnetism and Josephson effect of quantum tunneling had been discovered at subsequent researche in superconducting materials.Superconducting materials are widely used in energy,transportation,information and other fields owing to these three excellent electromagnetic properties.However,the large-scale application of superconducting materials was seriously restricted because of the low working temperature which come into the costly and scarcity liquid helium.In 1987,the discovery of YBCO superconducting material with critical temperature higher than liquid nitrogen temperature（77K）significantly reduced the application cost of superconducting material.The high and new technologies have been proposed forward one after another based on bulk YBCO such as superconducting suspension train,capture field magnet,superconducting motor and superconducting flywheel,which has produced huge social and economic benefits.At present,the traditional YBCO superconducting bulk materials are mainly prepared by"top-down"processes such as top seed melt texture,melt texture growth and powder melting.YBCO superconducting bulk that prepared by the above method were confronted with many problems,such as cumbersome process,long cycle,single shape,microcracks,poor mechanical properties and so on.In addition,the emerging application with superconductors,such as portable superconducting devices and superconducting gyroscopes that can be used in aerospace,require that superconductors not only have high critical current,but also have the characteristics of light weight.On the other hand,the advanced devices also need the superconductors to have some complex and controllable shapes,which are difficult to meet by traditional preparation processes.In addition,YBCO superconductor is a typical oxide ceramic.Its features of rigidity and brittle seriously restrict the potential of engineering application.Therefore,how to achieve YBCO superconductor Toughening without reducing superconductivity has always been a challenge in the field of engineering applications.This doctoral paper closely focuses on the above problems.First,an efficient fabrication of YBCO superconductor with ultralight,high-quality and shape controllable was developed based on 3D printing.The centimeter level superconducting bulk and gyroscope were prepared,which realized the suspension and rotation under liquid nitrogen temperature（77K）.Then,a plate interlocking double network composite superconducting material was formed by using low-temperature epoxy resin impregnation technique,combined with 3D printing process,which significantly improves the fracture toughness of the superconducting material;Finally,the preparation of YBCO superconductor line by improved 3D printing process is explored,and the superconducting core wire with consistent grain orientation is obtained.The paper mainly involves works as follow:1.The advanced independently building 3D printing manufacture facility has realized the preparation of superconducting bulk and superconducting aerospace gyroscopes with ultra light and high performance.The green slurry with excellent rheological and plastic properties was prepared through mechanical regulating and controlling.The centimeter level YBCO bulks with any complex shape was realized by the direct writen 3D printing technology,combined with the flow rate controlling parameter.The microstructure control strategy of low temperature cold casting was introduced to solve the problem of microcracks in the traditional preparation of YBCO bulk.The synchronous process of sintering and oxygen supplement was proposed.Its can greatly reduce the preparation time more than 85%compared with the traditional process of superconductor.The prepared YBCO bulk has the advantages of ultralight（density 1.38g/cm~3）and high current density（critical current value 5562A/cm~2）.A centimeter level superconducting aerospace gyroscope was prepared which realized the suspension and rotation under liquid nitrogen temperature.2.The strengthening and toughening of 3D printed YBCO superconducting bulk is realized by microstructure regulation.Firstly,the microstructure of 3D printed YBCO bulk was regulated by three-dimensional low-temperature cold casting,and the quasi isotropic uniform and orderly lamellar skeleton structure was obtained.Then,the low-temperature reinforced epoxy resin was evenly impregnated into the whole lamellar skeleton structure by vacuum assisted to form a double network structure with lamellar interlocking,which realized the preparation of high-strength,high toughness and ultralight YBCO composites.The results all suggest that the strengthening and toughening of YBCO bulk could be realized and the superconducting properties of these sample was without degradation.The mechanical strength and unit fracture energy could reach 412 MPa and 638.6 KN/m~2 at liquid nitrogen temperature,respectively.Compared with the superconducting material prepared by top seed melt texture,the strength and toughness were increased by 1.94times and 14.8 times,respectively.3.The preparation of YBCO superconducting core wire by 3D printing technology was explored.Researchers long believe that YBCO superconducting materials was difficult to prepare superconducting core wires because the existence of high angle grain boundaries that are difficult to eliminate in the phase formation process of YBCO superconducting materials.Finally,this paper explored the progress conditions of preparing YBCO superconducting core wire by 3D printing technology.The results showed that the micron superconducting core wire with good crystal orientation could be formed under appropriate temperature and tensile conditions,and the grain size was uniform with the plane size about 3-6μm and thickness about 2μm.At the same time,a printing needle integration for the preparation of YBCO stranded wire was designed. |
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